Biology subjects

Quek, L.-E.

Publications and source records attributed to Quek, L.-E..

12 recordsLinked to original sources

bioRxiv2026

Developmental stage-dependent decoupling of molecular and phenotypic responses to heat in wheat grain

Heatwaves during flowering and grain development threaten global wheat production, yet the extent to which developmental stage shapes molecular and phenotypic responses remains unclear. Here, we investigated whether heat stress (36/29{degrees}C for 48 h) imposed at closely spaced developmental stages surrounding anthesis generates stage-specific molecular responses that are associated with subsequent effects on grain properties. Heat exposure increased floret abortion most strongly when it was imposed at the trinucleate stage (TN; [~]48%) compared with the binucleate (BN) and early post-anthesis stages. Methylation levels were largely unaffected by prior heat treatments; however, heat induced stage- and locus-specific methylation changes, particularly at BN. Spatial RNA-seq revealed tissue-specific heat responses that were distinctively different in BN and TN. Integrated metabolomic analyses revealed stage-dependent metabolic reprogramming, including shifts towards stress-associated pathways. Despite heat stress at BN generating broader molecular reprogramming in developing grain, exposure at TN produced stronger effects on grain set and composition, revealing a decoupling between the magnitude of responses and phenotypic outcomes. Together, these findings demonstrate that subtle differences in developmental stage influence the complex molecular responses to heat and subsequent grain properties.

plant biology↗

bioRxiv2024

CD38 mediates nicotinamide mononucleotide (NMN) base exchange to yield nicotinic acid mononucleotide (NaMN)

Nicotinamide mononucleotide (NMN) is a widely investigated metabolic precursor to the prominent redox cofactor nicotinamide adenine dinucleotide (NAD+), where it is assumed that delivery of this compound results in its direct incorporation into NAD+ via the canonical salvage / recycling pathway. Surprisingly, treatment with this salvage pathway intermediate leads to increases in nicotinic acid mononucleotide (NaMN) and nicotinic acid adenine dinucleotide (NaAD), two members of the Preiss-Handler / de novo pathways. In mammals, these pathways are not known to intersect prior to the production of NAD+. Here, we show that the cell surface enzyme CD38 can mediate a base exchange reaction on NMN, whereby the nicotinamide ring is exchanged with a free nicotinic acid to yield the Preiss-Handler / de novo pathway intermediate NaMN, with in vivo small molecule inhibition of CD38 abolishing the NMN-induced increase in NaMN and NaAD. Together, these data demonstrate a new mechanism by which the salvage pathway and Preiss-Handler / de novo pathways can exchange intermediates in mammalian NAD+ biosynthesis.

biochemistry↗

bioRxiv2024

Cis-vaccenic acid is a key product of stearoyl-CoA desaturase 1 and a critical oncogenic factor in prostate cancer

Altered monounsaturated fatty acid (MUFA) metabolism is a hallmark of oncogenic transformation. Recently, the MUFA cis-vaccenic acid (cVA) was identified as a putative regulator of prostate cancer cell viability. cVA production requires the activity of stearoyl CoA desaturase 1 (SCD1), an enzyme frequently dysregulated in cancer, but the role of cVA in regulating cancer cell phenotypes has not been extensively explored, compared with the more commonly studied product and structural isomer of cVA, oleic acid. Here, we utilised SCD1 inhibition to study the effects of cVA in prostate cancer cells. We found that cVA consistently rescues reductions in cell viability due to SCD1 inhibition and promotes cell growth under normal conditions, thereby identifying cVA as an important and previously unrecognised product of SCD1 in prostate cancer. More broadly, we demonstrate that individual MUFA species exert a diverse range of influence on oncogenic phenotypes, highlighting a need to more precisely characterise the lipidome of cancer cells to understand the molecular pathology of the disease.

cell biology↗

bioRxiv2024

Fatty acids are not a significant contributor to the TCA cycle in cancer cell lines: evidence of incomplete fatty acid oxidation.

Upregulated fatty acid oxidation (FAO) is a hallmark of many aggressive cancers and is widely presumed to fuel the tricarboxylic acid (TCA) cycle for ATP production. However, the quantitative relationship between FAO capacity and its contribution to mitochondrial metabolism relative to other fuels remains unclear. Here, we combined parallel stable-isotope tracing with metabolic phenotyping across a diverse panel of 27 cancer cell lines to reveal a fundamental capacity-contribution paradox. Despite exhibiting FAO rates that varied over eight-fold, exogenous long-chain fatty acids consistently contributed minimally (<10%) to TCA cycle intermediates in all cancer cell lines. We demonstrated that FAO functions as a compensatory source of acetyl-CoA in cells with limited glucose-derived acetyl-CoA synthesis, rather than acting as a primary fuel source. In this context, high FAO rates do not primarily result from FAO-mediated suppression of glucose oxidation, but instead reflect the recruitment of fatty acid- and glutamine-derived carbons via a malic enzyme-dependent shunt to sustain the mitochondrial acetyl-CoA pool while preserving glucose-derived anaplerotic flux. These findings challenge the prevailing view that FAO serves as a primary bioenergetic fuel in cancer, instead identifying it as a compensatory rheostat that supplements acetyl-CoA supply in glucose-limited settings by working together with glutamine-driven, malic enzyme-dependent anaplerosis, providing a mechanistic framework to reinterpret the efficacy of FAO inhibitors beyond simple caloric starvation.

cancer biology↗

bioRxiv2024

Macropinocytosis mediates resistance to loss of glutamine transport in triple-negative breast cancer

Triple-negative breast cancer (TNBC) relies on glutamine uptake by the transporter ASCT2 to sustain their unique glutamine metabolism and growth. Despite previous data showing cell growth inhibition after ASCT2 knockdown, ASCT2 CRISPR knockout was well-tolerated by breast cancer cell lines. Despite the loss of a glutamine transporter and low rate of glutamine uptake, intracellular glutamine steady state levels were higher in ASCT2 knockout compared to control TNBC cells. Proteomics data revealed upregulation of macropinocytosis, reduction in glutamine efflux and glutamine synthesis in ASCT2 knockout cells. Loss of ASCT2 in TNBC cell line HCC1806 induced a 5-10-fold increase in macropinocytosis across 5 separate ASCT2 knockout clones, compared to a modest 2-fold increase in the shRNA ASCT2 knockdown. By comparison, ASCT2 knockout impaired cell proliferation in a non-macropinocytic breast cancer cell line, HCC1569. These data suggest that macropinocytosis provides a novel resistance mechanism to strategies targeting glutamine uptake alone. Despite this adaptation, TNBC cells continue to rely on glutamine metabolism for their growth, which suggests therapeutic targeting may need to focus on downstream glutamine metabolism pathways.

cancer biology↗

bioRxiv2024

Pathway metabolite ratios reveal distinctive glutamine metabolism in a subset of proliferating cells

Large-scale metabolomic analyses of pan-cancer cell line panels have provided significant insights into the relationships between metabolism and cancer cell biology. Here, we took a pathway-centric approach by transforming targeted metabolomic data into ratios to study associations between reactant and product metabolites in a panel of cancer and non-cancer cell lines. We identified five clusters of cells from various tissue origins. Of these, cells in Cluster 4 had high ratios of TCA cycle metabolites relative to pyruvate, produced more lactate yet consumed less glucose and glutamine, and greater OXPHOS activity compared to Cluster 3 cells with low TCA cycle metabolite ratios. This was due to more glutamine cataplerotic efflux and not glycolysis in cells of Cluster 4. In silico analyses of loss-of-function and drug sensitivity screens showed that Cluster 4 cells were more susceptible to gene deletion and drug targeting of lactate and glutamine metabolism, and OXPHOS than cells in Cluster 3. Our results highlight the potential of pathway-centric approaches to reveal new aspects of cellular metabolism from metabolomic data.

cancer biology↗

bioRxiv2024

CPT1a regulates the delivery of extracellular fatty acids for cardiolipin turnover in prostate cancer cells.

Mitochondrial fatty acid oxidation (FAO) has been proposed to be a major bioenergetic pathway in prostate cancer. However, this concept fails to consider FAO relative to other mitochondrial substrates. Here, we found extracellular long-chain fatty acids (LCFAs), including palmitate, stearate, oleate, linoleate, linolenate, are minor sources of carbon entering the TCA cycle compared to glucose and glutamine in prostate cancer cells, despite being assimilated in the mitochondria as acyl-carnitines. In contrast, cardiolipins were a prominent LCFAs sink, with some species achieving greater than 50% 13C-labelling within 6 hours, suggesting high cardiolipin turnover using extracellular LCFAs. Knockdown of CPT1a, the rate-limiting enzyme of LCFA entry into mitochondria, reduced the incorporation of extracellular linoleate into cardiolipins. These results demonstrate that FAO is not a major input for the TCA cycle and provide evidence for an underappreciated role for CPT1a in regulating LCFAs entry into mitochondria for cardiolipin remodelling.

cancer biology↗

bioRxiv2022

ACSM1 and ACSM3 regulate prostate cancer fatty acid metabolism to promote tumour growth and constrain ferroptosis

Prostate tumours are highly reliant on lipids for energy, growth and survival. Activity of the androgen receptor (AR) is associated with reprogramming of lipid metabolic processes in prostate cancer, although the molecular underpinnings of this relationship remain to be fully elucidated. Here, we identified Acyl-CoA Synthetase Medium Chain Family Members 1 and 3 (ACSM1 and ACSM3) as AR-regulated mediators of prostate cancer metabolism and growth. ACSM1 and ACSM3 are upregulated in prostate tumours compared to non-malignant tissues and other cancer types. Both enzymes enhanced proliferation and protected PCa cells from death in vitro, while silencing ACSM3 led to reduced tumour growth in an orthotopic xenograft model. We show that ACSM1 and ACSM3 are major regulators of the PCa lipidome and enhance energy production via fatty acid oxidation. Metabolic dysregulation caused by loss of ACSM1/3 led to mitochondrial oxidative stress, lipid peroxidation and cell death by ferroptosis. Conversely, over-expression of ACSM1/3 enabled PCa cells to survive toxic doses of medium chain fatty acids and promoted resistance to ferroptosis-inducing drugs and AR antagonists. Collectively, these studies uncover a new link between AR and lipid metabolism and position ACSM1 and ACSM3 as key players in prostate cancer progression and therapy resistance.

cancer biology↗

bioRxiv2022

Insulin sensitivity is preserved in mice made obese by feeding a high starch diet

Obesity is generally associated with insulin resistance in liver and muscle and increased risk of developing type 2 diabetes, however there is a population of obese people that remain insulin sensitive. Similarly, recent work suggests that mice fed high carbohydrate diets can become obese without apparent glucose intolerance. To investigate this phenomenon further, we fed mice either a high fat (Hi-F) or high starch (Hi-ST) diet and measured adiposity, glucose tolerance, insulin sensitivity and tissue lipids compared to control mice fed a standard laboratory chow. Both Hi-ST and Hi-F mice accumulated a similar amount of fat and tissue triglyceride compared to chow-fed mice. However while Hi-F diet mice developed glucose intolerance as well as liver and muscle insulin resistance (assessed via euglycemic/hyperinsulinemic clamp), obese Hi-ST mice maintained glucose tolerance and insulin action similar to lean, chow-fed controls. This preservation of insulin action despite obesity in Hi-ST mice was associated with differences in de novo lipogenesis and levels of C22:0 ceramide in liver and C18:0 ceramide in muscle. This indicates that dietary manipulation can influence insulin action independently of the level of adiposity and that the presence of specific ceramide species correlate with these differences.

physiology↗

bioRxiv2020

Nicotinamide mononucleotide (NMN) de-amidation by the gut microbiome and evidence for indirect upregulation of the NAD+ metabolome

Oral administration of nicotinamide mononucleotide (NMN) is a prominent strategy to elevate nicotinamide adenine dinucleotide (NAD+) levels to treat age-related pathologies, where it is assumed to be directly incorporated into the NAD+ metabolome through the canonical recycling pathway. During oral delivery, NMN is exposed to the gut microbiome, which can modify the NAD+ metabolome through enzyme activities that are not present in mammals. Here, we show that orally delivered NMN can undergo direct deamidation and incorporation in mammalian tissue via the de novo pathway, and that this deamidation is reduced in animals treated with antibiotics to ablate the gut microbiome. Further, we show that antibiotics treatment increases the overall availability of NAD+ metabolites in the gut epithelium, with one possibility that the gut microbiome could be in competition with the host for dietary NAD+ precursors. Together, these data highlight previously undescribed interactions between orally delivered NMN and the gut microbiome.

biochemistry↗

bioRxiv2020

A feedback loop between the androgen receptor and 6-phosphogluoconate dehydrogenase (6PGD) drives prostate cancer growth

Alterations to androgen receptor (AR) signalling and cellular metabolism are hallmarks of prostate cancer. This study uncovers a novel link between AR and the pentose phosphate pathway (PPP) through 6-phosphogluoconate dehydrogenase (6PGD), an androgen-regulated gene that is upregulated in prostate cancer. Knockdown of 6PGD impairs growth and elicits death of prostate cancer cells, at least in part due to oxidative stress. Targeting 6PGD using 2 specific inhibitors, physcion and S3, was efficacious in multiple models of prostate cancer, including aggressive castration-resistant models. Importantly, S3 also suppressed proliferation of clinical patient-derived explants (PDEs). Mechanistically, 6PGD decreased expression and activity of AR in cell lines and PDEs, revealing a novel positive feedback loop between these factors. The enhanced efficacy of co-targeting AR and 6PGD further supported the biological relevance of this feedback. This work provides insight into the dysregulated metabolism of prostate cancer and supports investigation of co-targeting AR and the PPP.

cancer biology↗

bioRxiv2020

EXERCISE-INDUCED BENEFITS ON GLUCOSE HANDLING IN A MODEL OF DIET-INDUCED OBESITY ARE REDUCED BY CONCURRENT NICOTINAMIDE MONONUCLEOTIDE

ABSTRACTObjective Almost 40% of adults worldwide are classified as overweight or obese. Exercise is a beneficial intervention in obesity, partly due to increases in mitochondrial activity, with a potential role for the concomitant increase in nicotinamide adenine dinucleotide (NAD+). Recent studies have shown that increasing NAD+ levels through pharmacological supplementation with precursors such as nicotinamide mononucleotide (NMN) improved metabolic health in high fat diet (HFD) fed mice. We examined the combined effects of NMN and treadmill exercise on the metabolic dysregulation in HFD-induced obesity.Methods Five-week old female C57BL/6J mice were exposed to control diet or HFD. Mice fed HFD were treated with NMN in drinking water (400mg/kg; HNMN), treadmill exercise (HEx) or combined NMN and exercise (HNEx).Results Unexpectedly, NMN administration impaired several aspects of exercise-induced benefits in HFD mice, including glucose tolerance, glucose stimulated insulin secretion from islets and reduced hepatic triglyceride accumulation. Mechanistically, HNEx mice displayed increased antioxidant and reduced prooxidant gene expression in both islets and muscle, suggesting that altered redox status is associated with the loss of exercise-induced health benefits with NMN co-treatment.Conclusion Our data show that NMN treatment blocks the beneficial metabolic effects of exercise in a mouse model of diet-induced obesity in association with disturbances in redox metabolism.HighlightsNMN dampened exercise-induced benefits on glucose handling in diet-induced obesity.NMN administration in exercise enhanced ratio of antioxidants to prooxidants.We suggest NMN administration may not be beneficial when NAD+ levels are replete.Competing Interest StatementL.E.W. is an inventor on patents licensed to Metro Biotech NSW and to Jumpstart Fertility, and has received sponsored research funding from both companies. He is an advisor and shareholder in EdenRoc Sciences (Metro Biotech NSW, Metro Biotech, Liberty Biosecurity), Life Biosciences LLC and its daughter companies (Jumpstart Fertility, Continuum Biosciences, Senolytic Therapeutics, Selphagy, Animal Biosciences, Iduna) and in Intravital Pty Ltd. L.E.W. provides consulting work for Life Biosciences.View Full Text

physiology↗